Radio receiver volume control circuit



Nov. 18, 1941.

J. c. COE 2,262,757

RADIO RECEIVER VOLUME CONTROL CIRCUIT Filed OCt. 16, 1940 f2@ f .d .u HSI W mosss'vi mfsa R2 Rl y 'Jmzxsmm :E LE- .1.'

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iE- E CAI HODE GIRCUH TRC INVENTOR JAMES C. COE

BY y n ATTORNEY Patented Nov. 18, 1941 RADIO RECEIVER VOLUME CONTROL v CIRCUIT James c. coe, Arungzn, va.-

Appucation october 1s, 1940, serial No. 361,357

12 claims. (ci. 179-1) Y (Granted under the m t: March 1883, as. amended April 3o, 192s; 37o o. G. '157) This invention relates specically to volume controls for radio receiving apparatus, it being an object of the invention to provide a system whereby the output level of various loads connected in parallel across the output terminals of a receiving or amplifying device may be individually adjusted, within certain limits, without affecting the output level of the other loads connected thereto.

It is a further object of this invention to provide a system whereby adjustment of the volume means of one control to any desired level between extremes, and the output of the other headset can be set by means of the control to any decontrol to various loads connected in parallel across the output terminals of a receiving or amplifying device may be independently. made for each load, without materially affecting the total impedance across the output terminals.

In the type of installation to which this speciiication particularly relates, the adjustment oi the volume of one of the loads such as a speaker or headset, will aiect the volume of the other speaker or headset loads connected in parallel therewith. In such an installation it is nearly impossible, particularly when many loads are provided, to maintain the output level in one load constant, without continual adjustment. It is an object of this invention toovercome the above disadvantage or diiiiculty encountered in this type of installation by providing a means coincident with the operation of the volume control means which will change the receiver or ampliiler output to accommodate the increase or decrease in output level.

This is accomplished in the control to one headset by an adjustable attenuating resistor or network which is connected between the receiver output and the headset, and is combined me'- chanically with a receiver gain or sensitivity control, which may take the form of a variable resistor which may be connected in the cathode circuit of certain tubes of the receiver, although other means for controlling the sensitivity, known in the art, may be provided; a second and similar arrangement applies to the second control ofl a second headset and includes an adjustable attenuating resistor or network between the receiver output and the second headset, this resistor or network being mechanically connected to a variable resistor which is connected electrically in parallel with the receiver gain or sensitivity control resistor of rst control.

In the embodiment illustrated there is shown a device which provides means for obtaining individual control of the output of a radio receiving apparatus to two loads such as headsets.

sired level between extremes, also the output level in one headset may be radically diierent from that in a second headset. Having once established the desired'level in the two headsets by.

means of the two controls, if any change in the output level to one headset becomes desirable, it may be accomplished Without producing any appreciable effect upon the level in the second headset. A

With the foregoing and other objects in view, the invention consists in the construction, combination and arrangement of parts hereinafter described and illustrated in the drawing, in which: l

Fig. 1 is a wiring diagram showing they connections for a plurality of headsets connected in parallel to the output terminal of a radio receiving set;

Fig. 2 is a wiring diagram showing a modification of the connections illustrated in Fig. 1, wherein the total impedance across the output terminal remains substantially constant for all adjustments.

In the circuit shown in Fig. 1, RI is a series variable resistance connected between the receiver output terminals and the headset load HSI. R2 is a variable resistor connected to terminals leading to the receiver cathode circuit.

The two resistance elements RI and R2 are each provided with an adjustable arm. These yarms are mechanically coupled but electrically insulated so that moving the control of one resistance element in a direction to short out more resistance will also cause the arm of the other 'Ihe output to one headset can be adjusted by 55 resistance element to move in a direction shorting out more of its resistance. Thus with less resistance between the headset load HSI and its receiver output, the load drawn by the headset HSI is increased. To supply this increase in load under normal conditions of operation, well below the receiver overload condition, the resistance R2 connected to the terminals leading to the receiver cathode circuit is also decreased, thereby increasing the kreceiver sensitivity or.

gain. In the embodiment illustrated by Fig. 1, there is also connected in shunt across the receiver output terminals a second headset load HSa. This headset load also has connected in series therewith a variable attenuating resistor Ra. The variable resistance Rb is connected to the terminals leading to the receiver cathode circuit. 'I'he resistance Ra and Rb are both provided with an adjustable arm. These arms are also mechanically but not electrically coupled so that movement of one arm to increase or decrease the resistance of one element will cause a similar increase or decrease in the other resistance element. as is apparent from Fig. 1

. and the description set out above.

'l'he change in setting of the resistor to HSI will have a slight eilect upon HSa', due to the change in` receiver sensitivity or gain caused by the change in the resistance in the receiver cathode circuit. 'I'his change will, however, be

smallwhen compared to the change produced upon headset load HSI, because RI is primarily applicable to headset HSI and is only secondarily applicable to vheadset H Sa, and because the receiver output regulation eects the change in the output voltage as it varies with the load, and the load varies with a change in RI. v

Readjustment of he control to headset HSa may, under some conditions, be necessary to obtain proper output level, particularly if the changes in RI and R2 have been relatively large. More than two loads may bev used, each with its control consisting of units similar to Ra and Rb or RI and R2. As explained above, the movement of a control to change the volume level in that headset produces some change in the volume level to the other headsets, but the greatest change will be produced in that one headset where it is desired. 'One control may be set to give maximum response in its headset, another control maybe set to give a much lower f response in its headset, and the remaining coniriggload, it is still possible to obtain a lower level ci response in the second load because of the attenuation available inthe audio circuit between the receiver output and that load. In other words, the receiver may be operated at a high sensitivity and low audio attenuation to Aone headset, and at a low power level in the second headset due to audio attenuation between the receiver output and the second headset.

jIf this deviceis used in moving vehicles such as airplanes, a certain amount of change of level in oneheadset only secondarily incidental to a work. It has been found from actual practice Vthat a maximum variation in the impedance oi the combination oil-ISI, RI, R2 and R3 of the order 3 to 1 may in some installations be entirely satisfactory, and will not produce van eiect appreciably noticeable to the ordinary hearing in the other headsets.

In Fig. 2, headset loads HSI and HSa are connected in shunt across the'output terminals of the receiver.4 The variable resistances R3 and Rc are eachv shunted directly across their rerespectiveheadsets, namely, HSI and HSa..

The value of the resistance elements R3 and Rc is determined largely trom the characteristics of the headsets HSI and HSa. It the impedance ratio of R3 to HSI is too high, control characteristics will not be smooth, since the impedance of the network would vary greatly with diilerent settings of the control, while if this ratio is too low, an excessive amount of incoming power from the receiver output would be wasted in heating resistance R3, similarlyv with Rc. The proper impedance ratio is determined between these extremes to give the best engineering compromise betweenfairly constant impedance and waste of power. l

The headset loads HSI and .HSa each have connected in series therewith a mesh circuit comprising the resistance RI, R2, R3 and Ra, Rb, Rc, respectively. The resistance elements RI and R3, as well as Ra and Rc, are variable, each being provided with an adjustment arm. These greater change of level produced in another headset may not bev serious enough to require readjusting the level to the first headset, but an extreme change in the level to one headset may require readjusting thelevel tothe other headset somewhat, in order to maintain the proper value.

arms are electrically and mechanically connected together so that as RI is increased an increasing portion of the resistance R3 is connected in a branch of the mesh circuit including the resistance R2 and in series with resistance RI. A circuit can also be traced from the receiver output in shunt across the headset HSI and includes a portion of resistance RI and a portion of the resistance R3 not lconnected in the aforementioned mesh circuit. The variable resistance elements R4 and Rd lare each connected to the terminals leading to the receiver cathode circuit. Each resistance element has an adjustment arm associated therewith, the adjustment arm of R4 being mechanically but not electrically connected to the adjustment arms of RI and R3, so that as the resistance of the mesh circuit which is in series with the headset HSI is increased, the resistance `R4 in the cathode circuit oi the receiver or amplier is also increased. The adjustment arm ior resistance Rd is also mechanically but not electrically connected to the adjustment arms for resistance elements Ra and Rc.

In the position of maximum power delivered to headset HSI, for example, the adjustment arms of resistance elements RI, R3 and R4 are in their extreme clockwise position providing ,a shunt path shorting out the resistance elements RI and R2, leaving only HSI and R3 in parallel; in this position the resistance element R4 in the cathode circuit is also shunted. The impedance of such a combination may readily be determined by means of computations known to the art.

. In the position of the control for minimum power intoHSI the impedance of the network `consisting of HSI, RI, R2 and`R3 can be determined by consideringthe group consisting of HSI and R3 in parallel, and this group in series with R2. then with RI in parallel with the aforementioned series parallel 'combination' in order to obtain the impedance of the aforementioned group. The impedance of such a network may rasa-157 8 be determined by means of computations` known in the art. It is also to be noted that in this position the resistance element R4 is inserted into the cathode circuit decreasing the receiverv sensitivity or gain. y

With any intermediate .setting for power available to -either headset HSI or HSaI, the impedance of the group consisting of HSI, Ri, R2 and R3, or HSa,'Ra, Rb and Re, may be calculated by applying Kirchhois laws. by means well known in the art.

Fig. 2 has the advantage over Fig. 1 in that the load on the receiveroutput is relatively constant, regardless of thesetting of the controls. Changing the setting of one control vaffects the signal level in the other headset due tov change in receiversensitivity, but this change in the second headset is` much less than that produced in the rst headset Where the change is desired.

It should be clearly understood that in Fig. 2 resistors Ra, Rb and Rc perform vthe same function with respect to HSa as resistorsRl, R2 and R3 perform with respect to H Sl. y

While my invention has been described above -in connection with a `radio receiver having a cathode circuitfor sensitivity control, it is obviously applicable for use in connection with other receiving devices for electrical communications having sensitivity control circuits employing variable resistances. Loud-speakers and headsets are only two of the many types of sound reproducing devices that may be employed.

Other modifications and changes in the number and arrangement of the parts may be made by those skilled 'in the art Without. departing from the nature of this invention Within the scope of what is hereinafter claimed.

The invention described herein may be manufactured and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. I

Having thus set forth and disclosed the nature of this invention, what is claimed is:

1. In a control circuit of a radio receiving apparatus, the combination including, a sound reproducing device, an audio attenuator control therefor, a receiver sensitivity control, and means mechanically connecting the attenuator and sensitivity control together so that upon adjustment providing a decrease in the attenuation,

, the vreceiver sensitivity is increased.

2. In a control circuit of a radio receiving apparatus of the type having. a controllable cathode circuit therein, the combination which includes, plural sound reproducing devices, control means for at least one reproducing device permitting the adjustment ofA the output level of said device, and means coincident with the adjustment of said output control means preventing said adjustment from materially ailecting the output level to said other reproducing means, saidA last named'means including a variable resistor connected to the cathode circuit of said receiving apparatus.

3. In combination, a radio receiving apparatus having an output circuit, plural sound reproducing devices connected thereto, means for varying the volume of said reproducing devices while still maintaining the total impedance across the Voutput circuit substantially constant, and means operative with the adjustment of said volume control means for aecting the sensitivity of the receiving apparatus.

vnected in series with at least one of said load devices, terminals leading' to the cathode circuit of the receiving apparatus, a variable resistor connected to said terminals, adjustable contact arms for both of said resistors. said arms being mechanically connected together, whereby .the adjustment of one variable resistance will also eiect adjustment of the other variable resistance.

5. In combination, a plurality of sound translating devices, a common audio frequency supply means for said translating devices having a cathode circuit, lines connecting said devices to the common audio frequency supply means, a pair of terminals leading to the cathode circuit of said audio frequency supply means, a variable resistor connected to said terminals, a variable attenuator 4for at least one sound translating device comprising a plurality of impedance elements, one of said elements being variable and connected in shunt directly 'across the sound translating device, the other of said elements comprising a mesh circuit connected in series with the translating device, said mesh circuit including a fixed and a variable impedance element, the variableimpedance element connected acrossxthe translating device and the variable impedance element of the mesh circuit each having adjustable contact arms, said arms being mechanically connected tbgether so that in one extreme position the mesh`circuit impedance is shorted out, and means responsive to the adjustment of said contact arms which will change the resistance connected to said cathode circuit.-

6. In combination, a plurality of sound translating devices, common audio frequency supply means for said device having a cathode circuit, conductors connecting said devices to the common output terminal of said common source oi.'

audio frequency, a pair of terminals leading to' the cathode circuit of the audio frequency supply, a variable resistor connected thereto, a variable attenuator for at least one sound translating device, said attenuator comprising two variable resistors and a fixed resistor connected in the output circuit of the supply means, and means coincident with the adjustment of the Variable attenuating resistors which varies the resistor connected in the cathode circuit.

'7. In combination, a plurality of sound repro- Aducing devices, common audio frequencysupply means therefor having a cathode circuit, means connecting said devices to the output terminals 'of said audio frequency supply means, means permitting independent control of the output level to each of the sound reproducing devices without materially changing the total impedance offered by said reproducing device and itsA control means, said means comprising three variable v resistors connected together mechanically, two of said resistors being connected in the output circuit between the audio supply and the sound reproducing devices, the third variable resistor being connected in the cathode circuit of the audio supply.

8. In a control circuit of a radio receiving apparatus the combination including, a sound reproducing device, an audio attenuation control y therefor, a receiver sensitivity control means, and

4. In a radio receiving apparatus having a means mechanically connecting the attenuation control and receiver sensitivity control means to- 4 n 9,209,757 gether so that upon adjustment providing for a decrease in the attenuation. the sensitivity is increased.

9.' In a radio receiving apparatus, the combination-including an output circuit. plural sound reproducing devices connected in parallel across said terminals. means comprising an adjustable resistance network for varying the volume of said reproducing device from a maximum to a minimum without Vproducing a variation in the munications, an output circuit, a reproducing deimpedance oi said reproducing device and network greater than 3 to l, and means operative `with the adjustment ot said volume control means for controlling the sensitivity of said iadio receiving apparatus.

10. In an electrical communication system having an output circuit and a sensitivity control circuit, a plurality of sound reproducing devices connected in parallel vwith said output circuit,

variable attenuating means connected in the out-l put circuit o! at least one reproducing device, said means permitting the adjustment -oi the attenuation to said reproducing device without provice connected thereto, an adjustable attenuating means for said reproducing device. and separate means operative with said attenuating means for varying the sensitivity of said receiving device.

of said receiving device.

12.v In a receiving device for electrical communications. an output circuit, plural reproducing devices connected thereto, an adjustable attenuation means for at least one said reproducing device, and separate means -operative with said attenuating means for varying the sensitivity JAMES C. COE. 

